In a time division multiplexing (TDM) network, a plurality of transmitting devices execute time synchronization and frequency synchronization by producing clocks from data signals that are continuously transmitted. Examples of a standard for a synchronous transmission method to be used for TDM are synchronous digital hierarchy (SDH) and synchronous optical network (SONET).
With the wide use of the Internet, networks that support Internet Protocol (IP) are widely used. According to IP, data signals are asynchronously transmitted on a packet basis unlike TDM, and time synchronization and frequency synchronization are executed by different methods.
Examples of a standard for the time synchronization and the frequency synchronization that are based on IP are Network Time Protocol (NTP) and IEEE 1588-2008 (IEEE: The Institute of Electrical and Electronics Engineers, Inc.). A technique that is defined by IEEE 1588-2008 enables time synchronization with accuracy of microseconds and is expected to be applied to a synchronization process that is executed between base stations in a wireless network.
Examples of the related art may include Japanese Laid-open Patent Publication No. 2002-16637, and Japanese Laid-open Patent Publication No. 2003-216595.